Positioning systems may be used in a variety of contexts for positioning a workpiece with respect to a tool. For example, in laser processing systems, a workpiece is typically carried on a table and positioned, before a laser beam is brought to bear on the workpiece. Traditional positioning systems utilize X-Y translation tables, which may include stacked and split designs.
In a stacked stage positioning system, the lower stage supports the inertial mass of the upper stage, which supports a workpiece. Such systems typically move the workpiece relative to a laser beam. The upper stage and lower stage may provide motion control in orthogonal dimensions. In one implementation of a stacked stage design, the X-axis motion stage carries the Y-axis motion stage. In such a configuration, the X-axis motion stage typically has less acceleration and bandwidth because it carries the mass of the Y-axis motion stage. The Y-axis motion stage is typically lighter, and is able to deliver greater acceleration and bandwidth. Stacked stage positioning systems typically account for motion dynamics caused by the relative motion of one portion of the stage to the other. These motion dynamics may result in non-linear effects arising from the moving center of gravity of the X stage as the Y stage moves relative to the X stage.
In split axis positioning systems, the upper stage is not supported by, and moves independently from, the lower stage. The workpiece is typically carried on the lower stage while a tool, such as a fixed reflecting mirror and focusing lens, is carried on the upper stage. A split axis design decouples driven stage motion along two perpendicular axes lying in separate, parallel planes. A split stage design has a benefit of a kinematic loop between the two axes passing through the force frame, which is typically a heavy granite block; however, split stages may exhibit problems of repeatability between the upper stage and the lower stage. Both stacked or split stage designs exhibit bearing tolerance stack-up (i.e., each bearing contributes some uncertainty to a process), which limits the precision of the positioning system.